In order to study airborne bacterial community dynamics over Tokyo, including fine-scale correlations between airborne microorganisms and meteorological conditions, and the influence of local versus long-range transport of microbes, air samples were collected on filters for periods ranging from 48 to 72 h. The diversity of the microbial community was assessed by next generation sequencing. Predicted source regions of airborne particles, from back trajectory analyses, changed abruptly from the Pacific Ocean to the Eurasian Continent in the beginning of October. However, the microbial community composition and the alpha and beta diversities were not affected by this shift in meteorological regime, suggesting that long-range transport from oceanic or continental sources was not the principal determinant controlling the local airborne microbiome. By contrast, we found a significant correlation between the local meteorology, especially relative humidity and wind speed, and both alpha diversity and beta diversity. Among four potential local source categories (soil, bay seawater, river, and pond), bay seawater and soil were identified as constant and predominant sources. Statistical analyses point toward humidity as the most influential meteorological factor, most likely because it is correlated with soil moisture and hence negatively correlated with the dispersal of particles from the land surface. In this study, we have demonstrated the benefits of fine-scale temporal analyses for understanding the sources and relationships with the meteorology of Tokyo’s “aerobiome.”

14Recent progress in Next Generation Sequencing allows us to explore the diversity of airborne 15 microorganisms across time and space. However, few studies have used consecutive short-16 period samples to explore correlations between the seasonal variation of the microbiota and 17 meteorology. In order to understand airborne bacterial community dynamics over Tokyo, 18including fine-scale correlations between airborne microorganisms and meteorological 19 conditions, and the influence of local versus long-range transport of microbes, air samples 20 were continuously taken from a platform at the 458-m level of the Tokyo Skytree (a 634-m-21 high broadcasting tower in Tokyo) from August 2016 to February 2017. Predicted source 22 regions of airborne particles, from back trajectory analyses, changed abruptly from the 23 Pacific Ocean to the Eurasian Continent in the beginning of October. However, microbial 24 community composition and alpha and beta diversities were not affected by this 25 meteorological regime shift, suggesting that long-range transport from ocean or continent 26 was not the principal determinant controlling the local airborne microbiome. By contrast, 27 local meteorology, especially relative humidity and wind speed, had significant relationships 28 with both alpha diversities and beta diversity. Among four potential local source categories 29 (soil, bay seawater, river, and pond), bay seawater and soil were constant and predominant 30 sources. Statistical analyses suggest humidity is the most influential meteorological factor, 31 most likely because it is correlated with soil moisture and hence negatively correlated with 32 the dispersal of particles from the land surface. 33

Continuous observations of cloud droplet size distributions (DSDs) in low-level stratiform clouds have been conducted at a height of 458 m from Tokyo Skytree (a 634-m-high broadcasting tower in Tokyo) using a cloud droplet spectrometer. In this report, the characteristics of cloud parameters related to the cloud DSD from June to December 2016 are presented. The mean cloud droplet number concentration (N c), average diameters, and effective diameters of cloud droplets in non-drizzling clouds were 213 cm −3 , 7.3 μm, and 9.5 μm, respectively, which are close to the reported values for continental stratiform clouds. The relationship between liquid water content (LWC; g m −3), N c (cm −3), and radar reflectivity (Z ; mm 6 m −3) was estimated as LWC = 0.17 N c 0.50 Z 0.45 , with a coefficient of determination (R 2) of 0.93. The observed cloud DSDs were well fitted by a lognormal distribution, and the average median diameter of the fitted DSD was 6.6 μm.

Ice nucleating particles (INPs) originating from Asia are expected to have large impacts on aerosol-cloud-precipitation interactions on local, regional, and global scales. However, their seasonal variability is poorly understood. Here, we present a year-round record of atmospheric INPs measured on Tokyo Skytree, which is the world's tallest broadcasting tower located in the Tokyo Metropolitan area. The INP number concentrations showed relatively small variations in the temperature regime below −20°C, whereas the values were episodically enhanced by long-range transported Asian dusts. On the other hand, the INP spectra in the temperature regime warmer than −20°C exhibited measurable seasonal variations. Notably, the INP number concentrations in the temperature regime between −15°C and −10°C tended to indicate higher values in warm/wet seasons and lower values in cold/dry seasons. Our results suggest that Asian dust events and seasonal variations in certain particles of biological origin linked to local/regional meteorology might influence the seasonal trends of the INP spectra over the Tokyo Metropolitan area.

The seeder-feeder interactions (SFIs), where raindrops from upper clouds grow by accreting cloud droplets in the lower clouds, have been extensively studied. However, there are few studies on the modification of raindrop size distribution (DSD) through this process. In the present study, rainfall from the landfalling rainbands of a typhoon was observed using an optical disdrometer and an X-band polarimetric radar. Rainfall was classified into the following three types based on the DSD characteristics at the surface and the existence of a ρ HV minimum in the upper layer: convective rainfall accompanied by a melting layer (type SF), convective rainfall without a melting layer (type C), and stratiform rainfall with a melting layer (type S). Type SF rainfall was regarded as having undergone SFIs between stratiform precipitation and shallow convection. The DSD for SF type rainfall was characterized by more small-to medium-sized raindrops and a larger normalized intercept parameter than rainfall types C and S. An analysis using vertical profiles of radar-derived DSD parameters for type SF rainfall suggested that the median-volume diameter of raindrops increased by accreting cloud droplets in the lower clouds, and that small-to medium-sized raindrops were produced by a warm rain process and breakup of raindrops.

The National Research Institute for Earth Science and Disaster Resilience deployed a lightning mapping array (LMA) in the Tokyo metropolitan area in March 2017. Called the “Tokyo LMA,” it obtains detailed three-dimensional observations of the total lightning activity (cloud-to-ground and intracloud flashes) in storms. The network initially consisted of 8 receiving stations, expanded to 12 stations in March 2018. Real-time total lightning images were first opened on the webpage in Japan. Real-time observations from the Tokyo LMA will be used in nowcasting lightning hazards and mitigating lightning disasters. Archived data will be used to develop lightning prediction techniques and a lightning climatology for the Tokyo metropolitan area.

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